Can't decide what to choose between Open Sans and Lato just like many other designers and developers ? Here is a brief article which would help you to pick up a font for your next web project.
Fonts were and are integral part of a website designs. In today's modern web designing world, there are thousands of font available and two of the most used ones are - Open Sans and Lato. Both these fonts are sans serif typeface and extensively used worldwide. Both of these fonts are free and resemble to each other in a lot of features, which pushes the designer in a state of dilemma. So here is a quick review so sort this problem out.

Direct Comparison

First of all we would see the two fonts together for almost same font weights. The sole purpose of fonts are to make text look good so lets see side by side comparison of these fonts.

Different people have different taste and opinion of one would surely not be what the other thinks. So I would try my best to judge it in an unbiased way. In the above comparison I think that Lato provides a bit more variety in look eliminating the need of other fonts. Moreover it include Hairline font weight which is not commonly found in fonts. No doubt Open Sans looks good but due to the above mentioned advantage. The winner of this stage is Lato.

Speed Optimization

When it comes to font, the second thing we look at is its speed. Today's websites need to be fast loading and one would never want to load tons of fonts for making a site look good. Sacrificing speed for fonts is not always a good idea.

From the above images its quite clear that Lato is a quite heavier font compared to Open Sans. Open Sans is more than 3 times faster and light weight than Lato. So here the clear winner is - Open Sans

Character Sets

Some sites would need multiple scripts like Cyrillic etc. but there are not many fonts which provide sub sets. Here is a list of character sets the fonts Lato and Open Sans have.

Lato -

Latin

Open Sans -

Cyrillic Extended (cyrillic-ext)

Greek Extended (greek-ext)

Greek (greek)

Vietnamese (vietnamese)

Latin Extended (latin-ext)

Cyrillic (cyrillic

This section does not need few more words. Winner - Open Sans

Font Rendering and Readability

I checked both the fonts in a couple of browsers and I found a minor issue in the readability of Hairline font weight of Lato. But font rendering and readability defers from browser to browser, site to site and background to background. It maybe be that the hairline font weight looks better in dark background or so. You can know more about this topic at Typekit's Blog. They have put detailed posts regarding this topic and I highly recommend to read those posts. So as I said one could not determine a winner is this section here there is No Winner

Conclusion

Both the fonts are frequently used and sometimes together too. They have become an essential part of Flat UI Modern designs. It would be great if in the near future machines are preloaded with these fonts. Would help millions to save a fraction of a MB :P Coming to the point the winner of this comparison is Open Sans. Lato is not bad either but a point behind Open Sans. Both these fonts load your webpage with awesomeness.
Please See - All the data above are only acquired from Google Fonts and no other source. Thanks for reading.

Wow... these post really answer my question. I really need to think what font to use in my blog, whether Lato or Open Sans.... I already a little bit incline toward Lato, but after looking at the weight need to be load, I might need to reconsider and evaluate more...